Many types of hand tools such as knives and multitools incorporate folding mechanisms that allow an implement to be moved between a folded position in which the implement is safely stowed in the tool handle, and an extended position in which the implement is ready for work. One typical example of such a folding tool is a knife having a folding blade. The knife handle typically has two opposed handle portions defining a blade-receiving groove. A blade pivots on a shaft attached to the handle such that in a folded position the blade is stowed with the cutting portion of the blade retained safely in the groove, and such that in an extended position the blade is extended away from the handle, ready for use. Foldable knifes are ubiquitous.
To increase the safety of folding tools such as knives, many such tools incorporate locking mechanisms of one type or another. When the knife blade pivots into the open position, it's pivotal movement is stopped with a blocking mechanism such as a transverse blade stop pin housed in the handle. Often a locking mechanism is included that prevents the blade from unintentionally pivoting back from the open into the closed position. There are many types of locking mechanisms. One common type is a “liner lock.” This kind of mechanism relies upon a resilient lever formed as part of a handle liner. When the blade is pivoted to the open or extended position, the resilient lever engages a cooperatively formed shoulder on the blade and thereby locks the blade in the open position. Another typical locking mechanism is a cross-bolt mechanism such as that described in U.S. Pat. No. 5,822,866. As detailed in the '866 patent, which describes an automatic opening knife, the cross-bolt mechanism includes a locking body that has a cylindrically tapered side wall portion. When the blade is extended to the open position, the tapered side wall portion of the locking body is urged by a compression spring into a locking position in which the locking body wedges between an engagement surface on the blade and a bore in the handle to lock the blade in the open position.
There are other types of blade locks in addition to the locking mechanisms just described. Another common type of locking mechanism is called a “lock back” mechanism. While there are variations in the structure for a lock back, in most lock back mechanisms a latch bar held between the handles at the upward side thereof pivots on a pivot pin extending through the latch bar and having opposite ends connected to the handle halves. When the blade or other implement is in the extended position, a spring mounted in the rearward portion of the handle (between the handle halves) applies upwardly directed pressure on the latch bar rearward of the pivot, urging the forward end of the latch bar—that is, the end of the latch bar on the opposite side of the pivot pin from the spring—into a locking engagement with the blade. The forward end of the latch pin typically includes a portion that engages a notch in the blade tang. The blade is unlocked by pushing downwardly on the rearward end of the latch pin at a notch in the handles—against the spring force, to cause the forward end of the latch bar to pivot upwardly and disengage the blade tang. It will be appreciated that a significant amount of space is required to house the springs and associated structures used to drive such lock back mechanisms.
A very traditional multi-bladed folding knife known as the “Whittler Pattern” has three blades: a single primary cutting blade on one end, and two secondary blades on the other end. While these knives have been manufactured for many years, given structural constraints it has been difficult to make such knives with reliable locking mechanisms for the primary cutting blade.
There is a need therefore for improved locking mechanisms for folding hand tools, and in particular improved lock back mechanisms. Lock back mechanisms for multi-blade folders such as the Whittler Pattern are needed.
The present invention relates to a hand tool—typically embodied as a knife—that incorporates a lock back-type locking mechanism for securely locking the implement such as a blade in the open position, and for releasing the lock to allow the implement to be folded back into the closed position.